What do buffers do?

• A. They accelerate acid-base reactions.
• B. They resist changes in pH.
• C. They increase pH indefinitely.
• D. They only work at one pH.

Answer: (B)

Buffers resist changes in pH by containing a weak acid and its conjugate base (or a weak base and its conjugate acid) that can neutralize added acids or bases. When a small amount of acid is added, the conjugate base component consumes the extra H+ to form the weak acid, so the pH doesn’t drop much. When a small amount of base is added, the weak acid donates H+ to neutralize OH−, forming the conjugate base and keeping the pH from rising steeply. This buffering action is most effective within about one pH unit of the acid’s pKa, and there’s a finite buffering capacity determined by how much of the buffering pair is present. Buffers do not raise pH indefinitely, nor do they accelerate acid-base reactions, and they don’t operate only at a single pH.